T79. Muscle Velocity Recovery Cycles in Detection of Early Axonal Involvement in Guillain Barre Syndrome

Electrophysiological changes in Guillain Barre Syndrome (GBS) are usually first seen 2–3 weeks after disease onset. Therefore, the initial diagnosis may be uncertain and differentiation between the demyelinating (Acute Inflammatory Demyelinating Polyneuropathy-AIDP) and axonal (Acute Motor Axonal Neuropathy-AMAN) types may be difficult. Muscle Velocity Recovery Cycles (MVRC) enable in vivo assessment of muscle membrane properties. We aimed in this study to examine whether MVRC may detect early changes in patients with GBS and may enable differentiation between AIDP and AMAN. Nine patients with GBS symptoms (5 AIDP, 3 AMAN and 1 acute CIDP (chronic inflammatory demyelinating polyneuropathy)) and 24 age- and sex-matched healthy controls were prospectively included. In addition to conventional nerve conduction studies (NCS) and electromyography, all patients were examined by MVRC in the anterior tibial muscle using Qtrac-software in the 1st week of symptom-start. A 4th-week control examination by NCS and electromyography was done in all patients, while MVRC was done in 4 (3 AIDP and 1 AMAN). MVRC parameters consisted of muscle relative refractory period (MRRP) and early, late and residual supernormality after 1, 2 or 5 conditioning stimuli. None of the patients had spontaneous activity in the 1st week examination. MRRP was significantly prolonged in patients compared to healthy controls, and early and late supernormality after 2 and 5 conditioning stimuli were decreased (non-parametric t test, p < 0.001). These changes were only seen in 3 AMAN and in 1 acute CIDP, while MVRC parameters were normal in all patients with AIDP. AMAN patients were severely affected already during the 1st week and were at the intensive care unit. EMG in the 4th week showed spontaneous activity in 6 patients including the 3 AMAN patients with profuse denervation activity, while none of the MVRC parameters changed significantly (paired t-test, p > 0.05). Changes in MVRC already in the 1st week of symptoms before presence of spontaneous activity may suggest early detection of axonal involvement in GBS. Additionally, MVRC could distinguish AIDP from AMAN, however this could also be due to severity of the disease in these patients. These results may suggest the potential use of MVRC in clinics. Future studies are needed with larger patient groups.